IgA nephropathy is a disease of the kidneys which leads to loss of blood and protein in the urine and can lead to severe kidney failure even when it begins in childhood. Unfortunately, there is no proven treatment for IgA nephropathy, although a few reports have described the successful treatment of patients with this condition with either fish oil supplements or a medication called prednisone. Those taking part will be asked to participate in a 5-year clinical trial which will compare every-other-day prednisone or daily fish oil capsules with a placebo (a pill which contains no medicine) in the treatment of my IgA nephropathy. The purpose of this study to be the evaluation of whether fish oil supplements or alternate-day prednisone can prevent or slow the decline in kidney function expected in children, adolescents and young adults with moderate to severe IgA nephropathy. Neither the doctor or patient will be told which one of the three treatments they are taking.